SCIENTIFIC BASES. WOOD.



The attached photography corresponds on the Altarpiece of Sant Llorenç, one of the few ones that were not burned to the period of the War of Spain, 1936-39. Because of that the militiamen converted the church into quarters of surveillance of the government of the Republic, established in Valencia.
The Altarpiece is a work of one of the most successful architects of the baroque period Lleonard Juli Capús i Calvet, son of ONTINYENT and established in Valencia. You can observe a declination towards the right because of the attack of termites about the carrying structure of wood; it makes more of a decade, and which it was possible to halt. Compare with the line of union of the cornice on both sides, which it goes round for all the plant.
The disturbances of the wood come to a large extent because it is about a living being, these can affect their structural or aesthetic value, and in any case it is almost always about a series enough extense of negative factors that are unworthy it, although not all in the same proportion. Of the importance, in many cases it will be depending on the use that the wood is destined to and of the type of effort to which it is requested. We can divide them in: Anomalies, faults and alterations.

The anomalies and the faults are disturbances happened during the growth of the tree.

The anomalies are inherent to the regular and orderly growth of the fibres, how they can be: nucs, distracted choir and retwisted fibres.

The faults however, they upset the structural order and organically corresponds to the tissues or apart from them how, the double sapwood or whiteness, the exfoliation, etc, occurs among the bark...

The anomalies and the faults affect mainly:
ü The fibres.
ü The rings of growth.
ü The heart.

The anomalies are disturbances occurred later in the formation of the woody fabric. In this group they are included the several types of fenelles, the, etc, putrefaction... But we will include the putrefaction in the causes of ruin of the wood.

We enumerate also the series of conditions that a good wood has to gather:

ü straight Fibre.
ü Regularity in the annual rings.
ü Fresh colour.
ü Absence of fenelles and fisures.
ü Brilliant and silky surface in the slices on centime.

If a tree grows in a good terrain, well directed, without being overwhelmed by other, with good climate... their wood will be good as regards the disposition of fibres.
The rule UNE-56/509 describes, the local anomaly of the structure of the wood, as a storm cloud produced by a branch of a trunk that keeps on remaining encompassed in the same one as the successive growths of this are produced. Moreover it distinguishes the classes from following storm clouds:
1. Living storm cloud: it’s the one produced by a living branch.
2. Dead storm cloud: it’s the one produced by a dead branch.
3. Storm cloud interior or covered: it’s the format for a broken branch or cutting, which has remained in the inside of the trunk, completely covered by the new capes of wood.

The storm clouds can be adherent or loose. The rule UNE-56-521/72 describes as an adherent storm cloud like in that, the fabrics of which, they are solidary with those of the wood that surrounds it because of to be formed by a living branch. This last relationship confers it an absolute stability after elaborated the wood. Storm cloud is also called fixed for him, steady storm cloud or storm cloud lives.

It manifests itself loose or brittle as a storm cloud in that one in which that it produces it is not the fabric of the branch solidary with the wood that surrounds it and usually breaks away from this.

The branches have generally more density of fibres than the shaft and in contracting for the one dried up it will contract more than the wood that surrounds it will. In the dead storm clouds a dark ring about the storm cloud, formed by a substance of little cohesion, observes that the wood, remaining loose, disappears in drying.

The storm clouds are anomalies that alter the direction and the continuity of the fibres. Their importance will be depending on the place in which they introduce. When they present themselves in a piece that will work in compression, will not affect their presence for him a lot if this is long. If it works in traction, if that will be seen influenced, because the storm cloud supposes a lack of continuity of the fibre and also know that the form of collaborating to absorb this type of effort that has the wood it is precisely for the solidary work of all fibres. In flexion, they affect for him more in the zones of traction than in those of compression for the former considerations, and in the effort of blade it does not have practically any effect.
It is the wood the marrow of which moves back sensitively from the symmetrical axis of the trunk.
It can be owed in several circumstances: dominant winds, proximity of the rocky grounds, peripheral situation of the tree in the forest, etc. The wood has little elasticity and resistance, and gives her heterogeneity that she produces her on working it.
Those that are shown are designated like this interlaced in the wood. Also rehairy wood is the renown. The area remains “aborrellada” and their work makes difficult.
It’s the wood the fibres of which, in account of following the direction of the axis of the tree, they are ordered in the form of helix. It is because of the excessive growth of the peripheral fibres with relation with the interior ones, or can be to that the tree has their roots in a discontinuous, waterproof terrain and in another deep and fertile. It appreciates itself in a tree standing, because the bark is botched and is in a helical way. This wood is only useful to props, boards, planks and pillars of shoring up and propping.
Burl: it is the excrescence of the trunk in shape globular and smooth area, constituted by wood of fibres interwoven irregularly. It’s confused sometimes improperly with the warts.
Warts: it’s a woody protuberance, of diverse origin, produced in the trunk or branches of the you hoist, that it causes an alteration of the structure woody and as consequent, in wood of fibres braided about axis little of growth.
Even, become bent can be distributions in forms more abundant or in forms. They are a consequence of freezes, lack of air, of sun...
It’s the fault of the wood that consists in have, of its inside, a piece of bark. Their more severe consequence consists to being a focus of posterior infections, besides affecting in the resistance of the wood.
The faults of the choir are usually a sign of the old age of the tree, since like the sapwood it keeps on being lignified, the choir (more lignified portion) can be it so much that him crack, with the consequent harm of the heartwood. These cracks can take dispositions, in accordance with which we divide them in, different:

A- Split or starry choir, or crow's feet: it is the central part of the tree that it shows one or several radial, wide fenelles, which start from the marrow.
B- Quadrature or leg of hen: they are fenelles that looks, generally, old in the trees and that starts from the rings close of the marrow towards the periphery, remaining at radial distances of this. They usually show badly smell and being the beginning of the putrefaction of the wood.
The part of ring of the whiteness or sapwood how it is known is lignified with time passing being heartwood. However, if because of a strong climatic alteration the death is produced premises of a zone of the outer capes of a tree, in this zone, will not be lignified later, with which it will come off included in the heartwood a portion of whiteness that on to be sawing the tree and being sectioned, it will change of colour (way of recognition) and will rot, being able to affect this putrefaction in the rest of the piece. Of here their gravity.
This fault consists of an excess of whiteness, consequence of a lignifications slower of the normal one. People face in those trees planted in very humid or marshy terrains, which grow with great speed, usually.
Fault that consists of a lack of adhesion among the rings in some zone of the tree. It’s a consequence, very little resistant and little suitable in “esquadries” as well as in trunks.
Cavity handed, in the inside of the wood that contains resin. It’s a fault that is not perceived on sawing them; and if it shows in many of them, it affects the resistance of the wood.
The fenelles are longitudinal clefts produced by drying or by fissures.
A- Fenelles of fissures: fissures produced by the action of the cold that go from the periphery towards the choir of the tree and that keep on being narrowed as they are deepened.
B- Fenelles of drying: longitudinal fissures, which look external generally in the capes of the wood brought down, and which are owed in the contraction produced by drying.
C- Fenelles of solsida: longitudinal fenella that it pulling from the basis of the trunk, or of a branch, provoked by the tearing of the woody elements, in the fall.
D- Choir of solsida: the emptiness that is educated in the central part is from the trunk lowered, when on cutting the tree a splinter of the central part of the trunk comes off joined to the wedge.
The pathological agents of the wood can be from biotic or a biotic origin, operating both agents normally in intimate relationship.

The application of a suitable protective treatment implies a necessary knowledge of the wood, of their pathological agents, of the protective chemical products, as well as of the systems of application.

Characteristics of the wood to have in account:
It’s an important factor as for the pathological agents that him can to attack it, since the humidity can originate negative effects about the wood, as dimensional variations, presence of fungi and insects that deteriorate their structure.
The humidity is also conditioned by the type of protector to be used and their application.
The durability would be the resistance of the wood to be attacked by destructive organizations. It can not be said that a type of wood were more resistant than another yeast that we relate in a determinate destructive agent. If that it is necessary to highlight that it is more durable, the wood of whiteness is more attackable than the wood of heartwood.
The degree of permeability of a species of wood in another varies a lot. This factor is important to consider it when choosing their protection.
The abiotics agents can produce damages so much direct how indirectly case facilitating in last was the performance of the biotic agents.
ü chemical Agents: atmospheric pollutants, aerosol salts, can be acids, bases.
ü physical – chemical Agents: solar radiation.
ü physical - mechanics Agents : extreme temperatures, water, cyclical humidity, particles atmospheric, rubbing or friction.
On being the wood a porous material can absorb water causing dimensional changes and increase of weight. Another pathological importance would be that one that derives from a posterior attack of organizations that need the humidity to be able to develop.

The negative action of the humidity will come in relation in the degree of permeability of each kind of wood.

It’s necessary to have in account the presence of metallic elements in the woods that can produce in touch decolouration (faces in the ones brought about by the chromogens fungi) with the humidity.
The wood that is placed in places that these changes are exposed they can produce in the fenelles wood since the wood does not balance out in the middle (in the inside) with the same speed with which it changes thermal state for them. This can originate descents in the resistance from the wood, of the aesthetics of this and it can suppose the entry of several organizations of ruin.
In the wood in the inclemency these polluting can cause the discontinuity of the painting or varnishes originating with this fissures in these capes, adherence goes down of widespread in the wood, propitiating the entry of water and putrefaction in little accessible places visually.

Besides the superficial degradation that supposes also changes of colour in the wood.
The wood that stands in the inclemency and feels subdued in the solar radiation (jets U.V.), can suffer a grayish superficial decolouration and later a defibration or superficial fraying of the wood that with the help of the precipitation and wind, they can produce the weathering of the wood, that is that this suffer big superficial inequalities.

This process of defibration is due to the degradation of the lignin, main component of the cellular wall, because of the jets U.V.

The infrared rays can also produce damages in this material, increasing the temperature of the surface, influencing like this on the humidity and provoking fenelles that will favour the entry of water.
Destruction is one of the most important destructive agents of the wood being able to bring about their total. In this point it is necessary to distinguish among resistance to the fire and to reaction to the fire, it can be said that it’s the resistance to the fire of the wood good since on the contrary thermal coefficient is a material of low it has one badly reaction to the fire in reason of their characteristic of combustibility, calorific power, flammability, favouring the combustion.
These do not present a potential danger in the woods but is related with the attack a posteriori of the fungi that if that they are harmful. They usually turn up associated in the humid wood and in fungi chromogens. They can attack in the luxuriant woods as well as in the conifers. They feed on the substances of reservation, not to be frequent the attack to the lignin.

The main damages of these bacteria are:
ü Dark superficial colourings.
ü Conical depressions in the zone of lamella half.
ü Erosion in the distinct capes of cellular wall.
The fungi are micro organisms of vegetal origin that they live in saprophyte form or parasitic. For the development the concurrence of several factors is necessary:
Humitat (òptima entre el 35-50%), temperatura, (òptima per al seu desenvolupament entre 20-30%), aire ja que l'absència d'aquest fa que es paralitze la seua activitat i aliment, ataquen la fusta de forma enzimàtica fent-ho més a la blancor (albura) que al duramen.
Les fustes s'infecten per mitjà d'espores que són transportades pel vent, pels insectes per contacte directe o per les ferramentes de treball. Dins dels fongs tenim dos tipus principals:
Aquestos s'alimenten de substàncies que no repercuteixen en la resistència de la fusta, això sí, produeixen un canvi de coloració, sent la més comuna la coloració blavosa però també podem trobar coloracions roges, terroses, verdes o grogues.

Blavós: apareix en les fustes coníferes en la blancor o albura.

Coloració verda: la trobarem normalment en la fusta frondosa i en les resinoses.

Cor roig del faig: coloració rogenca en el cor d'aquesta espècie.
Aquestos, al contrari dels fongs cromògens, poden produir danys estructurals en la fusta, descomponent-la per complet. La fusta afectada en un principi canvia de color a un to més fosc, conforme va desenvolupant-se la putrefacció la coloració va tornant-se a rogenc o terrós, arribant-se al final a la disgregació total de la fusta amb la coneguda pèrdua de les característiques físic-mecàniques.

Podem trobar tres tipus de putrefacció:

Podridura blanca: ataquen a la lignina deixant la cel·lulosa. El residu que deixa és fibrós o alveolar de color més clar que la fusta.

Podridura terrosa: ataca a la cel·lulosa deixant a la lignina. El creixement presenta un color marró fosc i tendeix a clavillar-se perpendicular a les fibres. És la putrefacció més greu o perillosa podent reduir la fusta a pols.

Podridura blana: És un tipus de putrefacció terrosa que deixa la fusta blana després del seu atac.

Quadre 3.1. Fongs de putrefacció.

MECANISMES DE DESTRUCCIÓ DELS FONGS I CARÀCTERS D'IDENTIFICACIÓ FONGS DE PUTREFACCIÓ
DENOMINACIÓ	FONG	ALIMENT	LOCALITZACIÓ	GRAVETAT DEL DANY
Terrosa o cúbica color marró Cliviels transversals	Orde: Basidiomicets Gènere: merulius, coniophora, pora voporaria	Cel·lulosa Hemicel·lulosa	Blancor Coníferes i Frondoses	Pèrdua de pes Disminució de la capacitat mecànica
Blana Aspecte cúbic, si Està sec	Microfongs	Cel·lulosa	Blancor coníferes i Frondoses	Pèrdua de pes Disminució de la capacitat mecànica
Blanca, fibrosa deslignificant Residu blanquinós	Orde: Ascomicets Desenvolupament en paret cel·lular	Lignina	Blancor i duramen Coníferes i Frondoses	Ídem anteriors Molt perilloses

Els insectes més comuns que destrueixen la fusta són els següents:

Brostíquids: poca importància en la fusta posada en obra. Els danys els produeixen els insectes adults.

Anòbids: ataquen tant el duramen com la blancor de les fustes velles i seques, tant frondoses com resinoses. Les seues galeries són d'1 a 2 mm de diàmetre quedant obturades per serradura (corcó).

Líctids: s'alimenten de substàncies de reserva de la fusta, ataquen a la fusta seca. Les galeries són d'un diàmetre molt xicotet i s'obturen amb serradura molt fina (arna de la fusta)

Cerambícids: és el més estés i el que més dany pot causar, ataquen tant a la fusta en obra com la de peu, especialment la de pi. S'alimenten de substància de reserva i les seues galeries són el·lipsoïdals obturades amb serradura granulosa.

Escolítids i platipòdids: utilitzen la fusta com a refugi i no com a aliment. Les seues galeries no presenten serradura i estan tenyides de marró o negra.



Quadre 3.2. Insectes xilòfags

Famílies de Insectes	Nom comú	Fustes que preferixen	Grandària Adult, cicle	Requeriments	Secció de Galeries, residus	Perforacions
Anòbids (anobium punctatum)	Corc Comú	Blancor Frondoses Coníferes	3-5 mm 1-3 mm	HR 60%	Circular Serradura basta	1,5-2,5 mm
Anòbids (xestobium rufovil)	Rellotge de la Mort	Blancor Duramen Frondoses	6-9 mm 4 anys	Presència de fongs	Circular Serradura grossa	3 mm
Líctids (l.brunneus L.linnearis)	Arna	Blancor Frondoses	4 mm 1any	Midó 3% H > 32%	Circular Serradura fina	0,8-1,5 mm
Cerambícidos (hilotrupes bajulus)	Corc Gran	Blancor Coníferes	10-20 mm 3-11 anys	28-30 ºC H > 32%	Ovalat Serradura granulosa	5-7 mm

Prefereixen les fustes frondoses, produeixen pocs danys i són de grans mides.

Himenòpters: No solen atacar a la fusta serrada. Sinó la dels arbres en peu o l'acabada de tallar, sovint atacada pels fongs.
Isòpters (tèrmits): S'alimenten de la cel·lulosa, de qualsevol fusta, aniquilant els fragments més blans sent sobretot fusta. A Espanya només es donen dos tipus:
Tèrmits subterranis: Viuen en colònies els nius del qual estan fora dels edificis atacats, en estos edificis fan nius secundaris i galeries les quals romanen en un grau d'humitat i lluminositat òptim per al tèrmit, fins a arribar a la fusta. Les galeries tenen la direcció de les fibres i són difícils de descobrir perquè deixen una capa externa que les amaga.
Tèrmits de fusta seca: aquestes poden arribar a destruir la fusta sense que es note en l'exterior ja que taponen els orificis d'entrada. Igual que els tèrmits anteriors prefereixen les fustes blanes i humides. Aquesta espècie és exclusiva de les Illes Canàries.
Quadre 3.3. Tèrmits.

Famílies de Insectes	Nom científic	Nom comú	Fustes que preferixen	Grandària Adult Cicle	Reque-riments	Secció de les galeries, Residus	Perforacions
Isòpters	Reticulis termers Lucifug	Tèrmits	Blancor i Duramen	Viuen 6-9 anys	HR 95%	Cavernes	Accés 2 mm
Himenòpters	Sirex	Vespes Fusteres	Blancor Conífera			Circular	10 mm
Lepidòpters	Cossus cossus	Palometa De la Fusta	Blancor Frondosa. Roure,om	90 mm 3 anys		Ovalat	15 mm

Les aus que més atac produeixen són els anomenats pardals fusters encara que el dany es faria extensible a totes les espècies si parlem de degradació de la fusta a causa de les deposicions dels seus excrements, reduint la vida dels recobriments de la fusta.
Els mamífers que ataquen a la fusta són els de l'orde rodentia (rossegadors), poden produir dany en la escorça dels arbres, ocasionant un tipus de putrefacció de coloració groga-terrosa permetent l'entrada a altres tipus de podridures i/o putrefaccions.

Dins dels mamífers també podríem parlar de l'acció de l'home, incendis provocats, tales descontrolades...
S'agrupen en:

Mol·luscs: ataquen a tot tipus de fusta en contacte amb l'aigua salada.
Crustacis: produeixen un atac superficial, encara que massiu, resultant perillós.